Burner control



Jan. 26, 1943. G. HOLMES 2,309,317

BURNER CONTROL Filed May 29, 1940 INVENTOR Gifford I. Holmes ATTQRN EYPatented Jan. 26, 1943 BURNER CONTROL Gifford 1. Holmes, Minneapolis,Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis,Minn, a corporation of Delaware Application May 29, 1940, Serial No.337,852

15 Claims. (Cl. 158-28) The present invention relates to burner controlsand more particularly to a novel control circuit and mechanism whereby ahigh degree of safety is obtained.

In burner control circuits it is customary to provide some combustionresponsive device which controls a circuit upon the occurrence ofcombustion when igniting, or upon a flame failure when the burner is inoperation. In most instances these devices are adapted to complete acircuit when combustion occurs and maintain the circuit for normaloperation of the burner. In many instances these contacts freeze or weldtogether, in which case, if flame failure occurs there is no protectionagainst flooding the vicinity of the burner with highly combustiblefuel. Not infrequently, upon starting the burner after such a failure, aserious explosion or fire will result.

It is also customary practice to provide relay mechanisms which mayoperate on either high or low voltage to control the burner motorcircuit. These relays comprise many parts and add considerably to thecost of equipment. Safety switches are frequently combined with thecombustion device or the relay, also adding to this cost.

A prime object of the present invention is to provide a combined relayand safety switch for a burner control.

Another object is to provide a combustion responsive switch and circuitwhich will not cause an unsafe condition if the contacts thereof shouldstick or weld in closed position.

A further object is to provide a burner circuit wherein a closed coldstack switch is combined with a thermal relay and safety switch.

Other objects and advantages of the present invention will be in partobvious and in part pointed out in the accompanying specification andclaims.

For a complete understanding of my invention reference will be made tothe drawing, the single figure of which shows a diagrammatic burnercontrol system.

In the drawing, a burner control motor 5, which may be a motor for anoil burner or a gas valve motor, and an ignition means 6 are under thecontrol of a condition responsive device II). This condition responsivedevice may take the form of a thermostat comprising a bimetallic coilII, a. contact blade [2, and a stationary contact I3 which cooperateswith the contact blade I2 in controlling an electrical circuit. Acombustion responsive device generally indicated at ll is also providedin control of this electrical circuit and may take the form of a devicewhich is responsive to the radiant heat of the flame or of the conductedheat from the flame, or other conventional device, and isdiagrammatically shown as comprising a switch blade l5 which cooperateswith a stationary contact I6 which contact and blade engage each otherupon relatively cold temperature. This contact is adapted to be openedwhen the heat rises in response to combustion and closed in the absenceof combustion. The low voltage circuit which the condition responsivecontrol device l0 and the combustion responsive device ll are in controlof originates fro a transformer II which comprises a high vo tageprimary I8 and a low voltage secondary iii.

A combined heat motor relay and safety switch is generally indicated bythe reference character 20. The heat motor comprises a heater 2| whichmay be wrapped around or suitably arranged in proximity to a bimetallicstrip 22 which may be suitably secured to a bracket 23. Th heater 2| andthe bimetallic element 22 cooperate to cause the bimetallic element 22to warp towards the right upon energizatlon of the heater 2| and to warptowards the left upon deenergizaton thereof. The bimetallic strip 22 maybe pro 'ded with an opposed bimetallic strip to compensate for changesin the ambient temperature in a conventional manner which is well knownin the art and therefore not shown. The upper end 24 of the bimetallicstrip 22 engages an insulating abutting block 25 which is secured to acontact blade 26. The contact blade 26 is suitably secured to a mountingbracket 21. The blade 26 carries a contact 28 which is in cooperativerelationship to a contact 29 carried by a switch blade 30 that issuitably secured to a mounting bracket 3 I. These switch contacts 28 and28 are held in their closed position as long as the end 24 of thebimetallic strip 22 remains in abutting engagement with the insulatingblock 25. When the end 24 is moved from beneath the block 25 the switchblade 26 will move downwardly to separate the contacts 28 and 29. Aresetting mechanism is shown as comprising a push rod 36 which whenpushed upward raises the insulating buttons 31 and 38 to lift theswitchblades 26 and 30 and permit the end 24 of the bimetallic strip 22 tomove beneath -the insulating block 25 to reset the device after it hasbeen tripped. The insulating buttons 31 and 38 are so arranged inrelationship to the switch arms 26 and 30 that the contacts 28 and 28will be held in open position during this resetting operation.

The bimetallic strip 22 also serves as a relay to open and close amercury switch 45 carried upon an arm 4| that is suitably pivoted at 42.A connecting link 43, which is diagrammatically shown as a dotted line,connects the arm 4| to the bimetallic strip 22. It will be seen thatwhen the arm 4| is rotated toward the right, which will occur when thebimetallic strip 22 is heated, that the mercury switch 40 will be rockedin a counterclockwise direction to cause the mercury therein to flowtoward the left to bridge contacts 44 and 45 and cause energization ofthe motor 5 and ignition means 5. When the bimetallic strip 22 cools,themercury switch will be rocked in a clockwise direction to unbridgethe electrodes 44 and 45.

A pair of oppositely facing contacts 55 and 5| are mounted on thebimetallic strip 22 by flexible arms 52 and 55, respectively. Thecontact 55 cooperates with a stationary contact 54 which is closed whenthe bimetallic strip 22 is in its cold position (as shown). The contact5| cooperates with a stationary contact 55 which is closed when thebimetallic strip 22- is heated. The contacts 55 and 5| are so arrangedin relationship to the stationary contacts 54 and 55, respectively, thatthe contact 5| will engage the contact 55 before the contact 50disengages the contact 54. As will be hereinafter more particularlypointed out, the contacts 50 and 54 are adapted to intermittently makeand break, or fry, to energize and deenergize the circuit to the heater2|.

Electrical energy for consumption by the motor 5 and the ignition means5 as well as for the low voltage control circuit is led from somesuitable source of supply, not shown, through the line conductors 50 and5|. A circuit for the primary winding 8 of the transformer may be tracedas follows: from the line conductor 50 through wire 52, contacts 29 and25 of the safety switch 25, wire 53; primary windin l5 of thetransformer I1, and wire 54 to the other line conductor 5|. A circuitfor the motor 5 and ignition means 5 may be traced from the lineconductor 50 through wire 52, contacts 29 and 28 of the safety switch20, wire 55, electrodes 44 and 45 of the mercury switch 40 and wire 55to the motor and ignition means, wires 51 and 58, and wire 54 to theother line conductor 5|.

Operation With all of the parts in the position shown the spacethermostat I is in its satisfied or warm position and the combustionresponsive device I4 is in its cold position. Assuming now that thespace temperature falls and the contacts i2 and I3 are closed, anenergizing circuit for the heater 2| may be traced as follows: from thesecondary I! of the transformer I! through the conductor 15, contacts l2and I3 of the thermostat I0, conductor 1|, conductor I2, switch arm l5,contact l5, conductor I3, heater 2|, conductor I4 back to the other sideof the transformer secondary l5. When this circuit is completed theheater 2| will generate heat which will cause the bimetallic strip 22 towarp toward the right. Upon warping toward the right the arm 4| whichcarries the mercury switch 45 will be moved toward the right which willcause the mercury within the tube to bridge the electrodes 44 and 45.With these electrodes bridged the burner motor and ignition means willbe placed into operation through the circuit previously traced. When thebimetallic strip 22 moves toward the right the contact 5| will engagethe contact 55.

It is necessary for these contacts to engage before the switch blade I5disengages the contact II in the combustion responsive device |4. Ifcombustion takes place properly the switch arm l5 will move toward theleft to its hot position to break the connection with the contact It.With this circuit broken an energizing circuit for the heater 2| may betraced as follows: from the transformer secondary I! through conductor15, thermostat Ill, conductor H, conductor 15, stationary contact 55,contact 5|, flexible arm 52, bimetallic strip 22, flexible arm 52,contact 55, stationary contact 54, conductor 15, the heater 2|, and theconductor 14 back to the other side of the transformer secondary II. Itwill be noted that this energizing circuit for the heater 2| isdependent upon closure of both of contacts 5| and 55, and 50 and 54.Continued energization of the heater 2| will cause still furtherdeflection of the bimetallic strip 22 toward the right. After thecontacts 5| and 55 are in engagement the flexible arm 55 may bend towardthe left to permit further movement of the thermostatic strip 22 towardthe right. After a predetermined movement in which the contacts 55, 54and 5|, 55 overlap, the contacts 50 and 54 will separate to break theenergizing circuit above traced for the heater 24. When this circuit isbroken the bimetallic strip 22 will begin to cool to move back towardthe left and thus reengage the contacts 55 and 54. It is seen thereforethat the contacts 50 and 54 will intermittently make and break toenergize and deenergize the heater 2| when combustion properly takesplace and the contacts l5 and I5 within the combustion responsiveelement l4 are open. Under these proper operating conditions with thebimetallic strip 22 oscillating between these heater control contacts,the upper end 24 of the strip 22 will remain beneath the insulatingblock 25 which maintains the safety switch contacts 25 and 29 inengagement. Also when the operation is proper the electrodes 44 and 45of the mercury. switch 45 will be maintained in closed position by thisoscillating movement. When the contacts i2 and 12 of the thermostat l5separate, the control circuit will be broken and the bimetallic strip 22will cool down and move back to the position shown in the drawing, thusbreaking the motor and ignition circuit.

Assuming now that the thermostat ll closes its contacts I2 and II andcombustion does not take place due to ignition failure, in this eventthe contacts l5 and I5 of the combustion responsive device M will remainin closed position. With the combustion responsive device remaining inthis position a continuous circuit for the heater 2| may be traced asfollows: from the secondary of the transformer ll through conductor 15,thermostat l0, conductors II and I2, contacts i5 and I5 of thecombustion responsive device l4, conductor ll, heater 2| and conductor14 back to the other side of the secondary ll. Because no combustionoccurs contacts i5 and I5 will remain closed and the heater 2| will becontinuously energized through this circuit and not intermittently madeand broken by the action of the contacts 50, 5|, 54, 55 which arecarried by the bimetallic strip 22. The strip 22 will be heated up tosuch an extent that the upper end 24 will move toward the right and outof engagement with the abutting block 25, thus permitting the safetyswitch contacts 25 and 25 to separate. When these contacts separate thecircuit from the line wire 50 through conductor 5| will be opened andtherefore there can be no circuit to the primary of the transformer norto the motor or ignition means 6 until the safety switch has been resetby manually operating the resetting mechanism 35. Therefore it is seenthat, when the device has gone out on safety as a result of failure ofignition, manual attention must be given to the system before the systemcan be restarted.

It will be noted that, if the contacts l5 and |6 do not close uponcooling of the combustion responsive device H, the heater 2| cannot beenergized to start the burner motor 5. Also, if the contacts l5 and i6should freeze, or weld, together, the heater 2| would remain energizedto cause the safety switch to trip open. It is seen therefore that,whether the combustion responsive device i4 fails to function properlyeither on heating or cooling, the burner motor 5 will not be operated tocause a hazardous condition to result.

Assuming now that combustion has taken place but there is a combustionfailure or a flame failure and the room thermostat I0 is not satisfiedand the contacts l2 and I3 remain in closed position. From the previousexplanation of normal operation it will be understood that the contacts50 and 54 which are carried by the bimetallic strip 22 have beenoscillating at some predetermined intermittent position to maintain theupper end 24 of the strip 22 in abutting engagement with the insulatingblock 25 as well as maintaining the energizing circuit through theswitch for the motor 5 and the ignition means 6. When a flame failureoccurs the combustion responsive device it will cool off and causeengagement of the contact arm IS with the stationary contact Hi. Whenthese contacts are made a circuit for the heater may be traced from thesecondary of the transformer I9, conductor 10, thermostat l0, conductorsII and 12, contact arm l5, contact I6, conductor 13, heater 2| andconductor 14 back to the other side of the transformer secondary l9.This will result in continued, rather than intermittent, energization ofthe heater 2| and will cause the bimetallic strip 22 to warp toward theright out of engagement with the abutting block 25 to permit the safetyswitch contacts 28 and 29 to separate thus shutting down the system.Therefore it is seen that in the event of flame failure also, manualattention must be given to the system before it may be restarted.

While I have shown one form which my combined relay and safety switchmay take, it will be obvious that many modifications which make use ofthe principles disclosed in the embodiment shown will occur to thoseskilled in the art. It

is therefore to be understood I am not to be limited only by that formshown and described but by the spirit of the appended claims.

I claim as my invention:

1. In a fuel burner system, in combination, a burner motor for operatingmeans for delivering combustible fuel to a burner, a thermostatresponsive to the temperature in a space which is heated by said burner,timing means controlled by said thermostat, switch means operated bysaid timing means for controlling the operation of said burner motor, anormally closed biased to open safety switch in circuit with said burnermotor, said safety switch being maintained in closed position by saidtiming means when said burner is operating properly, combustionresponsive means including closed cold contacts in setiming means in amanner to cause said safety switch to be opened in the event of ignitionor flame failure within said burner, and means maintaining 'said timingmeans in position to maintain operation of said burner motor upon theestablishment of combustion and the resultant opening of the said closedcontacts.

2. In a. fuel burner system, in combination, a burner motor, an electriccircuit therefor, a movable control switch in control of said circuit, athermally warpable member for operating said switch, a heater adjacentsaid member for causing warping thereof, a thermostatic switch incontrol of said heater, 9. pair of-cooperating contacts carried uponopposite sides of said warpable member, said contacts cooperating withsaid thermostatic switch for causing said member to intermittentlyenergize and deenergize said heater to thereby cause said member tomaintain said control switch in energizing position, and a closed coldcombustion switch also in control of said heater.

3. In a burner control circuit, in combination, a burner motor, anelectric circuit therefor, a motor switch in said circuit, timing meansfor controlling said switch, a biased open safety switch held closed bysaid timing means, means including heating means for causing said timingmeans to close said motor switch, combustion responsive means cooperablewith said last means for controlling the operation of said timing means,contact means carried upon opposite sides of and moved by said timingmeans, fixed contacts cooperable with said contact means and saidheating means for maintaining said motor switch and said safety switchclosed, and combustion responsive means for rendering said timing meansoperative and inoperative.

4. In a heating system, in combination, a bumer motor for operatingmeans for supplying combustible fuel to a burner, an electric circuittherefor, an oscillatable switch in control of said circuit, a thermalmotor including a warpable member and a heater for oscillating saidswitch ries with said timing means for controlling said to energize anddeenergize said motor, a normally closed biased to open safety switch incircuit with said burner motor held closed bysaid warpable member, anenergizing circuit for said heater, a closed cold temperature responsivecontrol switch in control of said energizing circuit, a closed coldcombustion switch in said energizing circuit in series with said controlswitch for initiating operation of said burner motor by energizing saidheater, and intermittently engageable electrical contact means movableby said warpable member for intermittently energizing and deenergizingsaid heater to maintain said burner motor in operation, said combustionswitch upon continued closure being adapted to cause said heater toremain energized to heat said warpable member sufficiently to move saidmember so as to permit said safety switch to open.

5. In a heating system, in combination, a timer, an electric heater, acircuit for energizing said heater, a condition responsive controller incon trol of said circuit, said heater upon energization deliveringenergy to said timer to produce a timed movement thereof from an initialposition through an intermediate range of movement to a predeterminedlimit position, a closed cold combustion switch also in control of saidcircuit and cooperable with said condition responsive controller toinitiate operation of said heater; fuel supplying means, a. circuittherefor, a first switch in control of said circuit, a second normallyclosed biased to open safety switch in said circuit, said safety switchbeing maintained closed by said timer when said timer is in its initialor intermediate range of movement, but not when in its limit positionwhere said safety switch will be permitted to open to deenergize saidcircuit, and a pair of contacts operated by said timer for energizingand deenergizing said heater to maintain said timer in said intermediaterange of movement.

6. In a heating system, in combination, a timer, an electric heater, acircuit for energizing said heater, a first condition responsive switchin control of said circuit, said first switch having an active closedcircuit position and an inactive position, a combustion switch in saidfirst switch, said combustion switch being responsive to the presence ofa condition incident to combustion and having an active closed circuitposition when, the condition is absent and an inactive position when thecondition is present, said two switches cooperating in their activepositions to cause energization of said heater, and switch means movedby said timer and cooperable with said first switch after said secondswitch has opened in response to the establishment of combustion forcontrolling said heater after said heater is energized.

7. In a heating system, in combination, a timer,

an electric heater, a first circuit for energizing said heater, a firstcondition responsive switch in control of said first circuit, said firstswitch having an active closed circuit position and an inactiveposition, a second switch in said first circuit with said first switch,said second switch being responsive to the presence of a condition andhaving an active closed circuit position when the condition is absentand an inactive position when the condition is present, said twoswitches cooperating in their active positions to initiate energizationof said heater; a second circuit for energizing said heater, switchmeans moved by said timer and cooperable with said first switch forcontrolling said second circuit after said heater is energized; saidswitch means comprising a first contact in said second circuit which isengaged subsequent to the initial energization of said heater, and asecond contact in said second circuit in juxtaposed relationship to saidfirst contact, said second contact being adapted to alternately energizeand deenergize said heater after said second switch opens.

8. In a heating system, in combination, a timer, an electric heater, afirst circuit for energizing said heater, a first condition responsiveswitch in control of said first circuit, said first switch having anactive closed circuit position and an inactive position, a second switchin said first circuit with said first switch, said second switch beingresponsive to the presence of a condition and having an active closedcircuit position when the condition is absent and an inactive positionwhen the condition is present, said two switches cooperating in theiractive positions to initiate energization of said heater, a secondcircuit for energizing said heater, switch means moved by said timer andcooperable with said first switch for controlling said second circuitafter said heater is energized; said switch means comprising a firstcontact in said second circuit which is engaged subsequent to theinitial energization of said heater, and a second contact in said secondcircuit in juxtaposed relationship to said first contact, said second'contact being adapted to alternately energize and deenergize saidheater said circuit with after said second switch opens; a burner motor.a circuit for energizing said motor, an oscillatable switch moved bysaid timing means in control of said circuit, and connecting means forcausing energization of said circuit when said first and second switchesare in their active positions.

9. In combination, an electric switch, a thermal motor movable whenheated in a direction to open said switch, a single heater therefor, afirst energizing circuit for said heater, a pair of condition responsivemeans in series with each other for energizing said first circuit; apair of contacts operated by said thermal motor, and a second energizingcircuit for said heater, said second circuit being controlled by one ofsaid condition responsive means in series with said pair of contacts.

10. In combination, an electric switch, a thermal motor movable whenheated from an initial position through an intermediate range ofmovement to a limit position wherein said switch will be opened, aheater for said motor, first and second energizing circuits for saidheater, a first condition responsive device in control of both of saidcircuits, a second condition responsive device also in control of saidfirst of said circuits, said first circuit when energized causing saidthermal motor to move to said limit position to thereby open saidswitch, and control means operated by said thermal motor also in controlof said second of said circuits, said second circuit beingintermittently energized by said control means to cause said motor toremain in said intermediate range of movement when said first circuit isdeenergized.

11. An automatic burner control system comprising in combination, meanscontrolling the delivery of fuel to a burner for combustion, a timer incontrol of said fuel delivery means, said timer having a deenergizedposition in which said fuel delivery means is inoperative, a mainswitch, a closed cold combustion switch, means including said mainswitch and closed cold combustion switch for energizing said timer tocause it to move from its deenergized position to a second position inwhich it renders said fuel delivery means operative and later to a thirdposition in which it again renders said fuel delivery means inoperative,and means operable by said timer in the event that said combustionswitch opens while said timer is in its second position, for limitingthe delivery of energy to said timer to an amount just sufiicient tomaintain it in its second position.

12. An automatic burner control system comprising in combination, meanscontrolling the delivery of fuel to a burner for combustion, a timer incontrol of said fuel delivery means, said timer having a deenergizedposition in which said fuel delivery means is inoperative, a mainswitch, a closed cold combustionswitch, means including said main switchand closed cold oombustion switch for energizing said timer to cause itto move from its deenergized position to a second position in which itrenders said fuel delivery means operative and later to a third positionin which it again renders said fuel delivery means inoperative, andswitch means operated by said timer in the event that said combustionswitch opens before said timer moves into its third position, saidswitch means alternately making and breaking an energizing circuit tosaid timer to maintain said timer in its second position.

13. A fluid fuel burner control system comprising in combination, meanscontrolling the delivery of fuel to a burner for combustion, a timer,electrical means for energizing, said timer, a main switch, a closedcold combustion switch, means including said last named switches forenergizing said timer to cause it to move from its deenergized positionto a second position in which it renders said fuel delivery meansoperative to deliver fuel to said burner, third switch means closed bysaid timer when it is in its deenergized position, fourth switch meansclosed by said timer as it moves toward itssecond position, and meansincluding said third and fourth switches for energizing saidtimercindependently of said combustion switch which opens whencombustion has been established.

- 14. A fluid fuel burner control system comprising in combination,means controlling the delivery of fuel to a burner for combustion, atimer, electrical means for energizing said timer, a main switch, aclosed cold combustion switch, means including said last named switchesfor energizing said timer to cause it-to' move from its deenergizedposition to a second position in which it renders said fuel deliverymeans operative to deliver fuel to said burner, said timer moving to athird position upon continued energization in which it again renderssaid fuel delivery means inoperative to deliver fuel, a. third switchclosed by said timer when it is in its deenergized position, a fourthswitch closed by said timer as it moves to its second position, meansincluding said third and fourth switches for energizing said timerindependently of said combustion switch, said timer alternately openingand closing said third switch to alternately deenergize and energizeitself provided said closed cold combustion switch is open, whereby saidtimer remains in its second position so long as combustion is present.

15- A fluid fuel burner control system comprising in combination, meanscontrolling the delivery of fuel to a burner for combustion, a timer,electrical means for energizing said timer, a main switch, a closed coldcombustion switch, means including said last named switches forenergizing said timer to cause it to move from its deenergized positionto a second position in which it renders said fuel delivery meansoperative to deliver fuel to said burner, said timer moving to a thirdposition upon continued energization in which it again renders said fueldelivery means inoperative to deliver fuel, a

- thereby rendering said fuel delivery means inoperative, and meanspreventing said timer from again rendering said fuel delivery meansoperation without manual intervention.

GIFFORD I. HOLMES.

